In the processing of a substrate, e.g., a semiconductor substrate (or wafer) or a glass panel such as one used in flat panel display manufacturing, plasma is often employed. During substrate processing, the substrate (or wafer) is divided into a plurality of dies, or rectangular areas. Each of the plurality of dies will become an integrated circuit. The substrate is then processed in a series of steps in which materials are selectively removed (or etched) and deposited.
Typically, a substrate is coated with a thin film of hardened emulsion (such as a photoresist mask) prior to etching. Areas of the hardened emulsion are then selectively removed, causing parts of the underlying layer to become exposed. The substrate is then placed on a substrate support structure in a plasma processing chamber. An appropriate set of plasma gases is then introduced into the chamber and a plasma is generated to etch exposed areas of the substrate.
During an etch process, etch byproducts, for example polymers composed of Carbon (C), Oxygen (O), Nitrogen (N), Fluorine (F), etc., are often formed on the top and the bottom surfaces near a substrate edge (or bevel edge). Etch plasma density is normally lower near the edge of the substrate, which results in accumulation of polymer byproducts on the top and on the bottom surfaces of the substrate bevel edge.
Typically, there are no dies present near the edge of the substrate, for example between about 2 mm to about 15 mm from the substrate edge. However, as successive purposely deposited films and byproduct polymer layers are deposited on the top and bottom surfaces of the bevel edge as a result of several different deposition and etch processes, bonds that are normally strong and adhesive will eventually weaken during subsequent processing steps. The purposely deposited films and polymer layers formed near the bevel edge would then peel or flake off, often onto another substrate during substrate transport. For example, substrates are commonly moved in sets between plasma processing systems via substantially clean containers, often called cassettes. As a higher positioned substrate is repositioned in the container, particles (or flakes) of purposely deposited film and byproducts on the bevel edge may fall on a lower substrate where dies are present, potentially affecting device yield.
Dielectric films, such as SiN and SiO2, and metal films, such as Al and Cu, are examples of films that are purposely deposited on the substrates. These films can also be deposited on the bevel edge (including the top and bottom surfaces) and do not get removed during etching processes. Similar to etching byproducts, these films at bevel edge can accumulate and flake off during subsequent processing steps, thereby impacting device yield.
For advanced technologies, it is desirable to expand the usable areas on the substrate surface to the edge of wafer (or substrate). As mentioned above, there are typically no dies present near the edge of the substrate, for example between about 2 mm to about 15 mm from the substrate edge, which is also called the “edge exclusion zone.” Edge exclusion zone is a region, such as between about 2 mm to about 15 mm from the substrate edge, at the edge of the substrate that is not usable and does not have dies. For advanced technologies, the target is to have usable area expended to less than about 2 mm from the edge of the substrate to increase usable area on the substrate. Therefore, the edge exclusion zone is targeted to be less than 2 mm.
In view of the foregoing, there is a need for apparatus and methods that remove unwanted deposits on the bevel edge of substrates to reduce edge exclusion zone to be less than 2 mm from the edge of substrates. Such apparatus and methods would expand usable area and improve process yield on the substrate.